Today I was looking at PRISM 4 and how it uses MEF as its DI Container and I thought, wouldn’t it be cool if you could use the 2 together?
Update: Please also check out this post to see how you can use the same composition container for both PRISM and MEFedMVVM so that stuff like IRegionManager, IEventAggregator etc can be injected also in MEFed ViewModels
http://mefedmvvm.codeplex.com/workitem/15391
Why would it be cool?
PRISM brings to the table
– Region Manager
– Modules infrastructure
– Many other utilities and services that you can consume
MEFedMVVM brings to the table
– ViewModel injection in XAML
– Design Time vs Runtime services (so that you can inject design time services when in blend)
– ContextAware services such as IVisualStateManager
Having the 2 working together would be awesome. The question is can they work together?
…teasing… suspense … ok enough 
The answer is yes and very easily…
How to do it
In PRISM you need to create a bootstrapper that will basically compose your application. MEFedMVVM also has a sort of Bootstrapper where you can specify how you want to compose the MEF composition. So as such all you need to do is to have your PRISM bootstrapper also tell MEFedMVVM how to do the composition.
Let’s start by creating a PRISM bootstrapper
We need a class that inherits from MefBootstrapper and we will need to override a couple of methods. Here is the code to do this
public class Bootstrapper : MefBootstrapper
{
protected override void ConfigureAggregateCatalog()
{
this.AggregateCatalog.Catalogs.Add(new AssemblyCatalog(typeof(Bootstrapper).Assembly));
}
protected override void InitializeShell()
{
base.InitializeShell();
Application.Current.MainWindow = (Shell)this.Shell;
Application.Current.MainWindow.Show();
}
#region Overrides of Bootstrapper
protected override DependencyObject CreateShell()
{
return this.Container.GetExportedValue<Shell>();
}
#endregion
}
Now lets enable MEFedMVVM
In order to do this we will simple need to implement the IComposer interface from MEFedMVVM and then return the AggregateCatalog property (that is given to us by PRISM)
#region Implementation of IComposer (For MEFedMVVM)
public ComposablePartCatalog InitializeContainer()
{
//return the same catalog as the PRISM one
return this.AggregateCatalog;
}
public IEnumerable<ExportProvider> GetCustomExportProviders()
{
//In case you want some custom export providers
return null;
}
#endregion
In this case we will return null as the GetCustomExportProviders. This is a feature used if you have some custom ExportProvider you want MEFedMVVM to use.
The last step (which is the actual line of code to enable MEFedMVVM) is where we tell the MEFedMVVM LocatorBootstrapper to use this class as runtime composer.
protected override DependencyObject CreateShell()
{
//init MEFedMVVM composed
MEFedMVVM.ViewModelLocator.LocatorBootstrapper.ApplyComposer(this);
return this.Container.GetExportedValue<Shell>();
}
As you can see I have put that line of code in the CreateShell method so that the Composer is applied as early as possible so that all views can use MEFedMVVM.
Now you can start using MEFedMVVM as you would in a normal project… For example in the Shell you can say
<Window x:Class="MEFedMVVMAndPRISM.Shell"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Shell" Height="300" Width="300"
xmlns:mefed="http:\\www.codeplex.com\MEFedMVVM"
mefed:ViewModelLocator.NonSharedViewModel="ShellViewModel">
and the ShellViewModel would be
[ExportViewModel("ShellViewModel")]
public class ShellViewModel
{
public string Text { get; set; }
public ShellViewModel()
{
Text = "Hello from the ViewModel";
}
}
Of course here I am not really leveraging MEFedMVVM capabilities, yet the purpose of this post is not to show those capabilities but to show how you can use PRISM and MEFedMVVM together and take what is best from both. To read more on MEFedMVVM visit the codeplex site.
I create a small sample project to showcase both PRISM and MEFedMVVM working together.
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